The use of local oscillators in communications systems is well known. A typical wireless communications system consists of a transmitter, a receiver and communication channels wirelessly connecting the receiver to the transmitter. At the transmitter, an information bit sequence is coded and transformed into an analog waveform centered at baseband frequency, which is subsequently up-converted to be centered at a higher frequency in order to be sent over one of a number of predetermined radio frequency (RF) channels. At a given receiver, the RF received signal is down-converted to one or more successive intermediate frequencies (IF) before being converted to baseband frequency in the desired channel. The resulting analog baseband signal is then digitized and demodulated to yield the original information bit sequence. In a standard transceiver, analog local oscillators (LOs) are used to implement each IF down-conversion or up-conversion stage.
Currently, there is an interest in using the less congested 5725 MHz-5850 MHz frequency band for wireless communications. This frequency band, known as the Industrial, Scientific and Medical (ISM) band, is currently unlicensed. To utilize the less congested ISM band with the existing 2400-2488.35 MHz point-to-point radio base station infrastructure requires a radio converter to up-convert the 2400-2488.35 MHz band to the 5725-5850 MHz ISM band and to down-convert the 5725-5850 MHzISM band to the 2400-2488.35 MHz band. This radio converter requires a stable local oscillator with a frequency of about 3.34 gigahertz (GHz). The present invention allows the construction of such a stable local oscillator using existing low-cost components.